Apparatus for measuring ultraviolet radiations



May 14, 194D. Y T. R. PORTER Er Al. 2,200,853

APPARATUS FOR MEASURING ULTRAVIOLET` RADIATIONS Filed oct. 2s, 1957 INVENTOR f 2,' f?. Paf/f2? W, Jazar/4W BEWQJ mmm ATTORNEY Patented May 14, 1940 yinurl-:u STATES v PATENT OFFICE APPARATUS FOR MEASUR-ING ULTRA- VIOLET RADIATIONS .Application October 23, 1937, Serial No. 170,630

8 Claims.

This invention relates to apparatus for measuring ultraviolet radiations and is particularly adapted for the measurement of such when accompanying infra-red radiations and/or visible light.

The principal object of our invention, generally considered, is the measurement of ultraviolet radiations by a method in which the total, including the infra-red and/or visible radiations, is first determined and then what is left after the ultraviolet radiations are screened out, the diie'rence between the two readings being a direct indication of the amount of ultraviolet radiations.

Another obj ect of our invention vis the provision of apparatus for measuring ultraviolet radiations, which is particularly adapted for use when the intensity of such radiations is so low that the absorption factor of lters creates a problem in obtaining direct readings or measurements.

A further object of our invention is the measurement of ultraviolet radiations by rst changing them into visible light by means such as uorescent material, and then measuring such light by a suitable photovoltaic cell.

Other objects and advantages of the invention, relating to the construction and arrangement of the various parts, will become apparent as the description proceeds. Y

Referring to the drawing illustrating our invention:

Fig. 1 is an elevational view, partly in vertical section, of apparatus for practicing our invention.

Fig. 2 is a partial plan and partial horizontal sectional view of the apparatus shown in Fig. l.

Fig. 3 is an elevational view ci the composite lter used with the apparatus shown in Figs. l

and 2, looking at the ultraviolet transmitting glass therein.

Fig. 4 is a view corresponding 'to Fig. 3, but looking at the other side of the filter.

Fig. 5 is a diagrammatic view corresponding to Fig. l, but showing another embodiment of our invention.

Ultraviolet radiations received from many sources are usually accompanied by visible light and infra-red radiations. The use of lters for separating the different kinds of radiations to measure them individually is practical where there is suflicient intensity to allow for the absorption of the shorter wave lengths, but, where the intensity of the radiations is low, the absorption factor of the filter creates a problem in obtaining direct readings or measurements of thel ultraviolet radiations.

It has been found that a measurement of ultraviolet radiations can be made by placing a glass, or other transparent substance, coated with se-v lected fluorescent material, such as zinc silicate, on the side facing the light source, shielded from any extraneous light, and disposed immediately above or adjacent a suitable visible light-measuring photovoltaic cell, such as a copper oxide cell. to which is attached a microammeter.

The selected fluorescent material is responsive to the particular band, or range of ultraviolet radiations which it is desired to measure, and these radiations react upon the iluorescent material producing visible light to which the cell .is responsive.

The device is held close to the light source, shielded from all extraneous light, and a reading taken on the meter. A second reading is then obtained when a clear glass lter with a known cut-off value, which may be the glass with which 204 the iluorescent material is coated, is interposed between the source of radiations and the iluorescent screen. The difference between the rst and second readings is a direct measurement of the amount of radiation in the band, to which the fluorescent material is responsive, between the cut-off value of the glass lter down to the lowest radiations emanating from the light source, provided the fluorescent material is responsive to such lowest radiations.

Referring now to the drawing in detail, like parts being designated by like reference characters, and i'lrst considering the embodiment of our invention illustrated in Figs. 1 to 4 inclusive, there is shown a source I 0 of ultraviolet radiations, such as a discharge lamp, the envelope II of which transmits ultraviolet radiations which are to be measured. The lamp I0 is, in the present embodiment, disposed so as to close an aperture I2 in one end of an opaque walled box or u receptacle I3, the other end of which is provided with a holder I4 for a screen I5.

In the present embodiment, the screen I5 consists of a frame I6 holding two pieces of transw parent material, such as glass, or other vitreous 4,- material, designated by the reference characters o I'I and I8. The transparent material Il is desirably one that freely transmits ultraviolet light and may, for this purpose, be formed of quartz or ultraviolet high-transmission glass, The piece of glass I8 may be ordinary window glass, if such has the desired cut-off characteristics.

Between the pieces of glass I'I and I8 is a layer of fluorescent material I9, which, in the present embodiment, may consist of zinc silicate. As an -55 I ner.

- prising means such as a copper oxide cell or other photovoltaic cell 2l and a microammeter 22 with a pointer 23 and a scale 24, calibrated to read in the desired units of illumination. The photovoltaic cell portion ZI of the device 20 may be pivoted, as indicated at 25, to the indicating portion 22 of the instrument, so that the two may be folded together when not in use. The instrument is adapted for connection to the box or container I3 in any desired manner, as by means of pins 26 and 21 outstandingl therefrom and removably connected with respect to said box I3 by being receivable in notches 28 therein and locked in place by turning to the position indicated in Fig. 2.

The apparatus illustrated in Figs. 1 to l` inclusive may be used as follows:

'I'he source of ultraviolet light which is to be measured, in the present embodiment designated by the reference character I0, is energized, the composite filtering medium I5 being disposed in the position indicated in Fig. 1, so that the ultraviolet transmitting glass I'I faces the source o-f radiations. This gives a. reading on the scale 24 which will represent, the visible light radiated from source I and transmitted direct through I'I, I9, and I8, plus additional visible light which is radiated from fiuorescent material I9 by virtue of its having converted the ultraviolet radiations from source 4I() into visible radiations.

'I'he screen I5 is then removed from the conw tainer I3 and reversed so that the ordinary window glass, or other absorbing means I8 fo-r ultraviolet light, faces the source I0 of radiations. The means for transposing the positions of the sheets I1 and I8 in the present embodiment, comprises the handle 20 which may begrasped by an operator, sliding movement of the screen I5 being permitted by the holder I4. The ultraviolet radiations from the tube I0, which it is desired to measure, are then absorbed by the glass I8 before reaching the fiuorescent material so that no ultraviolet light, of the band to be measured, reachesthe fiuorescent material I9 to be converted into visible light, and only the visible light radiated from source IIl and transmitted direct through I8, I9, and Il reaches the photovoltaic cell 2I. The difference between the two readings is., therefore, a measure of those ultraviolet radiations', which excited the fluorescent material I9 in the first case, and which were absorbed by the ultraviolet screen I 8, in the second case. It is obvious that, by comparing this difference in readings with the readings of any other device which accurately measures ultraviolet radiations of the same wave length, at various degrees of intensity of these radiations, the scale 24v can be accurately calibrated in terms of the units of that other measuring device.

Referring now to the embodiment of our invention illustrated in Fig. 5, an apparatus is there shown which will do the work of that of Figs. 1 to 4 inclusive, but in a slightly different man- In this figure, the source of ultraviolet radiations may be a discharge tube Illa, as in thev preceding embodiment, said tube being disposed above the container I3a so as to allow the radiations therefrom to pass down to the bottom of said container and impinge on a coating I9a of a desired fiuorescent material which may be disposed on-a sheet II.2L of transparent material such as ordinary' window glass. Immediately below the sheet'of glass I'Ia is disposed a photovoltaic cell 2 Ia which may be a copper oxide photox cell, as in the first embodiment, connected to a microammeter 22a, having a pointer and scale as previously described;

A reading is first taken of the ultraviolet source Illa, allowing the radiations therefrom to impinge directly on the fiuorescent material Isa, While the device is, of course, shielded from all extraneous light, as by being used in a dark room. A second reading is then taken when a clear glass filter iSa is interposed above the fiuorescent material, said filter having the desired known cut-off value. As in the previous embodiment, this filter I8a may be made of ordinary window glass, if it is desired to measure the radiations below the cut-off value of such glass. The difference between the first and second readings is a direct measure of the ultraviolet light which excites the fluorescent material during the first reading and which is absorbed by the filter I8a during the second reading, and the intensity ofthis light may be determined by mere subtraction of the second reading from the first, after the scale of the microammeter 22a has been suitably calibrated by taking readings on sources of light of known intensity in the ultraviolet region being measured.

From the foregoing, it will be seen that We have devised a simplified apparatus and method for measuring the intensity of the ultraviolet radiations in a definite wave length range, which are generated by a given source, by converting said radiations into visible light and measuring the increase in visible light which is due to this conversion. Because we are measuring substantial quantities of light, it is-possible to secureaccurate readings and thereby determine the value of theselected ultraviolet radiations in the lsource with reasonable accuracy, even though said value may be small. This method is a considerable improvement over methods which attempt to yfirst filter out all radiations'other than ultraviolet, and then measure the ultraviolet radiations direct, particularly when the amount of ultraviolet radiations is small relative to the amount of otherv radiations.

Although preferred embodiments of our invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims'.

We claim:

1. Apparatus for measuring ultraviolet radia, tions comprising a photovoltaic cell and micro-- of material transparent to visible light covering said cell and coated on one side with iiuorescent material, in combination with removable means' for filtering out the ultraviolet light to be meassured,`from said radiations before it impinges on said iiuorescent material.

3. Apparatus for measuring ultraviolet radiations comprising a copper oxide photovoltaic cell yand microammeter, and a` screen disposed between the source of radiationsy and said` cell, said screen comprising a sheet of material transparent to ultraviolet radiations and coated with zinc silicate, a sheet of material which absorbs the ultraviolet radiations to be measured, and means whereby the positions of said sheets, with respect to said source and cell, may be transposed.

4. Apparatus for measuring ultraviolet radiations comprising a device for-measuring visible light,- and a screen disposed between the source vof radiations and said device, said screen comprising a sheet of material transparent to ultraviolet radiations and coated with fluorescent material, a sheet of material which absorbs the ultraviolet radiations to be measured, and means whereby the position of said screen may be transposed. v

5. A reversible screen for use in measuring `ultraviolet radiations, comprising a frame in which is mounted a sheet of material adapted to transmit ultraviolet radiations and a sheet of material which absorbs the ultraviolet radiations to be measured, and a layer of fluorescent material disposed adjacent a surface of said -ultraviolet transmitting sheet.

6. Apparatus for measuring ultraviolet radiations, comprising a light meterand a screen distering glass, a layer of fluorescent material therebetween, land means whereby the position of said screen with respect to such a light meter may be reversed.

8. Apparatus for measuring ultraviolet radiations, comprising a light meter and a screen disposed between the source oi radiations and saidA meter, said screen comprising a reversible duplex combination of a sheet of ultraviolet radiations transmitting material, a sheet of ultraviolet radiations filtering materaL'and a layer of fluorescent material therebetween.

THOMAS R. PORTER. WILLIAM L. SULLIVAN. 

